The present invention relates to a media access method for optical local area network (LAN) systems, and more particularly to a media access method combining packet exchange and line exchange by a wavelength-division multiplex method.
Signals transmitted over a transmission path from the transmitting side to the receiving side can be broadly classified into two categories. One comprises signals which require immediacy and interactivity, such as telephone signals and conference TV signals, and the other, signals which do not, such as data and computer programs. A network having an exchange function, such as a LAN, should desirably be able to handle both of these two categories of signals.
Meanwhile, the access method often used in a LAN is line exchange for the first category of signals, and packet exchange for the second. An optical LAN system integrating these line exchange and packet exchange methods is also known, referred to as the Fiber Distributed Data Interface II, or Or Well ring, which is described in the paper "Orwell; a protocol for an integrated services local area network" (Br Telecom J. Vol. 3, No. 4, October 1985, pp. 27-35.
This Orwell ring uses only one optical wavelength and a plurality of packets divided into packets for packet exchange and ones for line exchange. As a result, the transfer capacity of each group of packets is smaller than where packet exchange and line exchange are performed independently. Thus, in packet exchange, the throughput is reduced on account of a smaller number of packets that can be present on the system. In line exchange, the number of channels that can be taken is limited and, at the same time, the transmission rate per channel is considerably lower than the transmission rate of the system, making it impossible to transmit picture signals which require a high transmission rate.